Dopamine turnover in the mediobasal hypothalamus in rat fetuses

In this study, the dopamine turnover in the mediobasal hypothalamus, the ke y compartment of the neuroendocrine regulation of reproduction, was evaluat ed in fetal male and female rats. High performance liquid chromatography wi th electrochemical detection was used to measure 3,4-dihydroxyphenylalanine , dopamine and 3,4-dihydroxyphenylacetic acid in the mediobasal hypothalamu s of fetuses on the 21st day of intrauterine development and in primary cel l culture (cell extracts and culture medium) of the same brain region, expl anted at the 17th fetal day and maintained for seven days. The same techniq ue was applied to determine dopamine release from fetal neurons of the medi obasal hypothalamus in response to an excess of K+ in the perifusion system or in culture. L-3,4-Dihydroxyphenylalanine, dopamine and 3,4-dihydroxyphe nylacetic acid were detected both ex vivo and in culture. The ratios of the concentrations of L-3,4-dihydroxyphenylalanine/dopamine and 3,4-dihydroxyp henylacetic acid/dopamine were significantly higher in vitro than ex vivo, showing a lower rate of dopamine production and a higher rate of its degrad ation in the experiments in vitro. Moreover, it has been demonstrated that an excess of K+, i.e. a membrane depolarization, resulted in a highly incre ased release of dopamine in the perifusion system and in culture. The dopam inergic activity in the developing mediobasal hypothalamus showed sexual di morphism that was manifested in a greater concentration of 3,4-dihydroxyphe nylalanine and dopamine, at least in cell extracts of cultures, as well as in a higher rate of dopamine release, both in the perifusion system and in culture in males compared to females. Thus, dopamine is synthesized and rel eased in response to a membrane depolarization in the mediobasal hypothalam us of rats as early as the end of intrauterine development, suggesting its contribution to the inhibitory control of pituitary prolactin secretion. (C ) 1998 IBRO. Published by Elsevier Science Ltd.